The primary objective of this project is to determine the prevalence and the ages when progressive and/or delayed onset of sensorineural hearing loss (SNHL) is most likely to occur in infants and young children due to congenital cytomegalovirus (CMV) infection. Our project will also define risk factors in the newborn period that predict SNHL in CMV infected infants without clinically apparent disease. Our third aim will define the relative contribution of CMV infection to delayed onset hearing loss in the population. These aims will be achieved by identifying all newborns with congenital CMV infection from University Hospital and serially testing them to evaluate their hearing sensitivity at various ages. Also, a randomly selected control group of newborns who are CMV negative from the well baby nurseries will be followed and compared to CMV positive children without hearing loss at birth. All infants born at University Hospital are currently screened virologically for congenital CMV infection by the investigators of this proposal. At 3 weeks, 3, 6, and 12 months of age, each CMV positive infant will have a complete audiological evaluation by a clinical audiologist that will include an auditory brainstem evoked response (ABR) and immitance measures for each ear. Also, each child will have a complete audiological evaluation at 18, 24 and 30 months of age that will include behavioral audiometric assessment (visual reinforcement or play audiometry) and immitance measures to obtain pure tone thresholds, speech reception thresholds and speech discrimination scores. The control groups will receive similar audiological evaluations at 6, 12, and 18 months of age. Currently 49 newborns with congenital CMV infection and 178 controls have been enrolled in the first year. About 10% of the newborns with congenital CMV infection have SNHL, with both progression and delayed onset of hearing loss documented in the first six months of life. None of the controls have had SNHL in the first year of life. Our proposal will provide better knowledge of the epidemiology and natural history of SNHL due to CMV. This information is essential for planning early detection and intervention strategies for SNHL in infants and young children.